I am looking around for a replacement ECU for my 1994 K1100LT. On realOEM there are 2 main ones listed, namely 13611464710 and 13611464717, with the one ending in 717 being the KAT version. There are plenty of the 717 versions about on Ebay etc but the 710's seem rarer. So whats the difference? Could I put the KAT version (717) on my bike instead of the 710? Currently it has a ...710.

Don't think so.....
The non-kat has a different loom, and an adjustable resistor for the CO.
You really need the 710.

You 'could' use the catalyst version Motronic brain, IF you then weld, drill and tap threads for an oxygen sensor bung into your exhaust and fit a O2 sensor, then replace the simple engine loom (only) with a catalyst version, then also eliminate the now superfluous additional ignition box attached to the battery frame. This is what Big Block runs, and it's an easy job, and all parts were readily available at the time of the swap from the earlier style. Or just look for the correct ECU. 

All of the preceding tiddies of info are relevant if the bike in question was built prior to about the 7th month of 1993 when the Motronic units (and looms) changed.

Phil asked if I would check the ECUs I have but the one I have has 1 464 811 on it and when I put that into Real OEM it says it is for a 95 to 98 K1100 but if I go to the drill down I find no reference to that number. TWB can you explain this

RicK G wrote:Phil asked if I would check the ECUs I have but the one I have has 1 464 811 on it and when I put that into Real OEM it says it is for a 95 to 98 K1100 but if I go to the drill down I find no reference to that number. TWB can you explain this

Rick, I had a look around and it appears 1464811 was superseded by 13617651599 from 12/98 and is a "fully suppressed" motronic control unit to be used with a specified fuel pump MA 2.2. As such it may not work on mine unless I have that pump - which is unlikely. Phil

Rockman wrote:

RicK G wrote:Phil asked if I would check the ECUs I have but the one I have has 1 464 811 on it and when I put that into Real OEM it says it is for a 95 to 98 K1100 but if I go to the drill down I find no reference to that number. TWB can you explain this

Rick, I had a look around and it appears 1464811 was superseded by 13617651599 from 12/98 and is a "fully suppressed" motronic control unit to be used with a specified fuel pump MA 2.2. As such it may not work on mine unless I have that pump - which is unlikely. Phil

MA 2.2 refers to the Motronic 2.2 version such as was used on R850/R1100/later K1100, 2.1 being the version prior to 7/93 prod date K1100/K100-16V/K1, and version 2.4 on R1150 models.

I concur that 13 61 7 651 599 and 13 61 1 464 811 are one and the same. For kicks, there are 3 available of the 7 651 599 in Germany and they're a mere US$2052.08. 

..And, Rick, these are entirely different part numbers and their fitment specific to the '94 K1100 is unknown. BMW's ETK & AIR catalogues do not clarify.